Air lubricated planing hull



Nov. 14,1967 R, PAYNE 3,352,270

AIR LUBRICATED PLANING HULL Filed Aug' 19, 1966 INVENTOR PETER R. PAYNE swam, M BY J M ATTORNEYS United States Patent 3,352,270 AIR LUBRICATED PLANING HULL Peter R. Payne, Silver Spring, Md., assignor to Peter R. Payne Inc., Rockville, Md. Filed Aug. 19, 1966, Ser. No. 573,580 2 Claims. (Cl. 114-67) The present invention is directed to an air lubricated planing hull which reduces or substantially eliminates skin friction by interposing a layer of air between hull and water.

The rapid development of hydrodynamics in the 19th century enabled ship resistance to be separated into its various components for the first time. The realization that skin friction was the major component of resistance at low Froude numbers naturally lead inventive engineers and naval architects to explore ways of eliminating it. A review of the patent literature since 1850 shows an almost endless variety of systems devised to achieve this result. Most of them exploited the idea of air lubrication. It was well known that the drag reduction theoretically obtain-able by gas lubrication was proportional to the difference in the densities of gas and water. Air was the most attractive gas because of its availability.

Experiments with air lubrication may be divided roughly into two different types. In the first phase, from about 1840 to 1950, attempts were made to introduce a film of air between the water and a conventional ship hull. Somewhat overlapping this period and continuing up to the present day, radically different hull forms and air supply systems have been tried. Systems which have been reduced to practice to date include the Air Cushion Vehicle which achieves complete separation between hull and water, the Captured Air Bubble and various air lubricated planing hulls.

Usually, new surface effect vehicles have been initiated by engineers from disciplines other than naval architecture and it is often felt that many desirable features of conventional ship design are sacrificed in order to gain speed. Over-emphasis of the problem of reducing resistance has tended to lead to rather box-like craft which are undeniably capable of making high speed over relatively smooth water surface; but a successful boat or ship must be able to do much more than this. It must be able to survive a storm at sea and be capable of making an economically high speed through rough water without subjecting its occupants to physiologically intolerable accelerations. The conventional displacement hull is more influenced probably by such considerations than by speed alone.

Therefore, the present application is directed to the application of air lubrication principles to conventional hull structures without too much compromise of sea worthiness. Thus, the benefits of air lubrication may be achieved while still retaining the benefit of all the structural and sea-keeping features already built into conventional designs.

A prior form of air lubricated planing hull also in- -volves conventional planing hull design. In this instance, a false bottom of heavy nylon cloth is applied to the planing surface and provided with means for pressurizi-ng the space between the false and true hulls. Air leaking through the cloth separating the false hull from the water surface gives effective air lubrication. The heavy cloth which constitutes the porous membrane separating the captured air bubble from the water surface is stretched tight to conform to conventional planing hull lines. Although substantially 100% separation between the water surface and the cloth is achieved, such an approach requires an uneconomically high air supply pressure since this is virtually governed by the dynamic pressure corresponding to the stagnation streamline on the planing hull. Thus, the air pressure elsewhere in the cushion is too high. While this problem could be reduced by suitable compartmentation of the cushion, the air supply power requirement is still quite high. Moreover, although skin friction could conceptually be eliminated, this approach has no effect on the wave drag or the spray drag of a conventional planing hull.

Therefore, the present invention is directed to a false hull membrane which overcomes the problems encountered by the above-mentioned prior design. The false hull membrane of the present invention is quite baggy. This new concept is a form of captured air bubble and the bubble is essentially at constant pressure, resulting in minimum wave drag and virtual elimination of spray drag. It is estimated that the air supply power requirement is three BHP for each ton of displacement. This figure represents a considerable saving over the power requirement of the above-discussed prior art concept. Also, the propulsive power requirement is less because of reductions in both wave and spray drag. 7

It is contemplated that the baggy membrane of the present invention could be incorporated as conventional equipment on new boats or supplied in the form of a kit for modifying existing boats.

Other features of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principles of the invention and the best mode which has been contemplated of applying those principles.

In the drawings:

FIGURE 1 is a perspective view of a small boat provided with the baggy membrane on the hull thereof;

FIGURE 2 is a perspective view showing the interior arrangement of the boat shown in FIGURE 1;

FIGURE 3 is a schematic view showing the flow of water with respect to a conventional planing hull; and

FIGURE 4 is a schematic view showing the flow of water with respect to the constant pressure air-lubricated hull of the present invention.

The present invention is directed to an air lubricated planing hull comprising porous inflatable membrane means secured to the bottom of said hull and pressurized air supply means mounted on said hull and adapted to supply air to said membrane means to inflate said membrane means at a constant pressure while air is permitted to pass through said membrane means to provide a film of lubricating air between said membrane means and the water.

FIGURE 1 shows the small boat to which the device of the present invention has been applied. It is contemplated that the device of the present invention could be applied to boat hulls of many designs and the shape of the boat hull shown in FIGURE 1 is merely by way of example. The hull 10 is provided with a flat bottom 12 sloping upwardly at the bow of the boat. A bag-like structure 14 is secured to the bottom of the boat by any suitable means. In this example, a pair of substantially triangular shaped gussets 16 are inserted along the edges of the bag to give the bag the necessary fullness, but such gussets are not essential to all bag designs. The bag member is constructed of a porous, flexible material, such as nylon cloth, plastic or the like. The bag member covers substantially the entire rear half of the bottom surface of the boat since this is the portion of the boat which will remain in contact with the water when the boat is traveling at relatively high speeds. The bow half of the boat will be raised up out of the water and it is unnecessary to provide the bottom surface of this portion with the baggy membrane. On other boat designs, with diflerent characteristics, the percentage of the planing hull covered by the bag will naturally vary for the particular proportions.

The boat may be provided with any suitable means of propulsion, such as an outboard motor 18, which drives the propeller 20. An auxiliary power supply 22 is mounted in the bow of the boat to drive an air blower 24 which is connected to the conduit 26. The conduit 26 is in turn connected with the plenum chamber 28 which is mounted over the baggy membrane secured to the underside of the hullLThe plenum chamber 28 is in fluid communication with the baggy membrane 14 across substantially the entire width of the boat so as to achieve a uniform distribution of air to the membrane although this is not a necessary feature. The auxiliary power requirements for air lubrication are quite small and range in the area of 2 to 3 BHP per ton displacement. Thus, it is possible to drive the centrifugal blowers for the air supply from the main propulsion engines or a self-contained auxiliary power supply unit could be mounted in the boat as shown in the present example.

By itself, 100% effective air lubrication can only halve the total resistance of a planing hull. For further improvements to be obtained, it is necessary to find ways of reducing wave making drag and spray drag. Spray drag is directly due to the momentum dissipated in spray. Spray occurs when the planing surface is inclined at an angle to the free surface of the water. Wave making drag is associated with the static pressure distribution over the hull surface, and specifically, over the planing surface in the planing model For a conventional planing surface this pressure distribution is highly nonuniform, being a maximum at the stagnation point and falling otf to a very low value at the stern. Minimum wave drag is obtained when the pressure distribution is uniform and increases from this value with increasing 'nonuniformity of the distribution. Spray drag is affected in the same way and is essentially zero for the uniform distribution situation.

FIGURE 3 shows the relation'of a conventional planing hull 30 with respect to the water when the hull is in the planing position. The flow of the Water past the hull 30 is indicated by the arrows 32. The spray is indicated by the arrows 34 and is 'a directresult of the build-up of static pressure at the stagnation point 36.

FIGURE 4 shows the relationship of a constant pressure hull 40 embodying a'ba'ggymembrane 44 in accordance with theprinciples of the present invention. The hull 40 in FIGURE '4 is shown in the planing position with respect to the water and the flow of the water past the hull is indicated by the arrows 42. Utiliziiigthe baggy membrane of the present invention, the internal air pressure deflects the planing surface into an essentially constant pressure profile. The response rate of the membrane is high enough for it to change shape under the influence of waves to constantly retain a near-optimum profile under dynamic conditions.

In this manner, the baggy membrane of the present invention not only achieves substantially effective air lubrication but provides a constant pressure distribution over the planing surface which results in substantially reduced spray drag and wave making drag.

It is also contemplated that the principle of a flexible, porous bag which constantly leaks airto reduce skin friction could be utilized to construct an inflatable boat, raft or barge. Those portions of the bag material which are normally under water would be made porous and those portions of the bag material which are normally above water would be rendered air impervious. Such a raft or barge could be used for ferrying stores and other supplies. The supplies to be transported could be either set directly on the inflated bag member or some sort of rigid support structure could be secured to the upper surface of the bag member for the reception of the'supplies.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An airlubricated planing hull comprising porous inflatable membrane means secured to the bottom of said hull and pressurized air supply means mounted on said hull and adapted to supply air to said membrane means to inflate said membrane means at a constant pressure while air is permitted to pass through said membrane means to provide a film of lubricating air between said membrane means and the water.

2. An air lubricated planing hull according to claim 1 wherein the membrane means depends from and is secured to said hull about the edges thereof to cover substantially the entire rear half of the bottom of said hull.

References Cited UNITED STATES PATENTS ANDREW H; FARRELL, Primary Examiner. 

1. AN AIR LUBRICATED PLANING HULL COMPRISING POROUS INFLATABLE MEMBRANE MEANS SECURED TO THE BOTTOM OF SAID HULL AND PRESSURIZED AIR SUPPLY MEANS MOUNTED ON SAID HULL AND ADAPTED TO SUPPLY AIR TO SAID MEMBRANE MEANS TO INFLATE SAID MEMBRANE MEANS AT A CONSTANT PRESSURE WHILE AIR IS PERMITTED TO PASS THROUGH SAID MEMBRANE MEANS TO PROVIDE A FILM OF LUBRICATING AIR BETWEEN SAID MEMBRANE MEANS AND THE WATER. 